Single ended amplifier with double ended output



SINGLE ENDED AMPLIFIER WITH DOUBLE ENDED OUTPUT Original Filed Jan. 17, 1952 4 Sheets-Sheet 1 15 mm. REFERENCE v I mssme RELEASES '7 TORPEDO REFERENCE INVENIORS H. x. sxmnsmo CHARLES mwsuwsu 0 /3w,& E Z0 M ATTORNEYS Aug. 21, 1962 H. K. SKRAMSTAD ETAL 3,050,690

SINGLE ENDED AMPLIFIER WITH DOUBLE ENDED OUTPUT 4 Sheets-Sheet 2 Original Filed Jan. 17, 1952 mm mm INVENTORSI H. K. SKRANSTAD CHARLES RAUDENBUSH JOHN A. HART BY jMw/ZEM ENE-Juli 29.51am

Aug. 21, 1962 H. K. SKRAMSTAD ETAL 3,050,690

SINGLE ENDED AMPLIFIER WITH DOUBLE ENDED OUTPUT Original Filed Jan. 17, 1952 4 Sheets-Sheet 3 H m w my m0 5 m m. T M V T mm w M m& m R H M v K 5 AM 3 L N K M m%@ ww oon.m WI. 8;. 03M \E Y Q h k! m z: l 1% ml I 2N C Qhq M v. 05 m! xmv i 2 no x mm on \E l E I z. m! vv :0. 1 mm v- 0N- T z 9! I N; x 000 on V5 own m h\ a m M m at 3: com 32 oon+ g- 1962 H. K. SKRAMSTAD ETAL 3,050,690

SINGLE ENDED AMPLIFIER WITH DOUBLE ENDED OUTPUT 4 Sheets-Sheet 4 Original Filed Jan. 17, 1952 INVENTORS H. K. SKRAMSMD 3 55524 292223 %Ez8 21 ME:

CHARLES RAUDENBUSH JOHN A. HA T Patented Aug. 21, 1%62 assess 2 Claims. (Cl. 330--117) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. The present invention relates to a double ended linear amplifier used in an autopilot for controlling the flight of an aircraft or for directing and stabilizing the airfiight path of a guided missile. This application is a division of copending application Serial No. 266,978, filed January 17, 1952, for Autopilot, now Patent No. 3,011,738.

For information relating to the characteristics of the guided missile, in which the autopilot incorporating the instant invention is utilized, reference is made to the application of William H. A. Boyd, Serial No. 655,538, filed March 19, 1946, for Aircraft, and that of Dundas P. Tucker, Serial No. 204,057, filed January 2, 1951, for Method of Attack on Marine Targets and Missile Therefor, and that of William H. A. Boyd, Serial No. 200,680, filed December 13, 1950, for Guided Missile and Assembly Thereof.

One object of the instant invention is to provide single ended amplifiers with double ended output.

Another object of the present invention is a combination of two single ended amplifiers in specific cascade connection to provide a double ended output.

A further object of the present invention is to provide a two stage DC. amplifier having increased positive feedback to establish a higher gain.

Other objects and features will become readily apparent to those skilled in this art during the course of the following detailed description of one embodiment of the present invention, taken in connection with the accompanying drawings forming a part of this specification and in which:

FIG. 1 is an illustrative diagram of a selected altitude attack path of the missile from its release point in the air to the point at which it disgorges an explosive payload toward a surface target;

FIG. 2 is a block diagram of the overall autopilot circuits;

FiG. 3 is a detailed schematic diagram of an embodiment of the summation amplifier circuits; and

FIG. 4 is a block diagram representation of an embodiment of the control summation amplifier circuit employing the circuit of P16. 3.

Referring now to FIG. 1 showing an altitude program of the missile from the point at which it is released from the mother craft until striking the target, the missile is designated by the numeral 10, the mother craft by numeral 9, and the target by numeral If it be assumed the missile is released at the maximum abovemcntioned range and altitude, an altitude path substantially resembling that designated as 12 is preferably followed. After release at the relatively high altitude of point 8, an electrical signal is generated by an altimeter mounted within the missile. This signal is compared with a fixed reference, representative of a low altitude reference (point 16) and a signal representing the error between the missile altitude and this first reference altitude is sent to the missile outopilot which directs the missile to reduce this error to zero by seeking this reference altitude. For the illustration shown the missile is commanded to dive. Although at high release altitudes, as here shown, it is desired that the missile quickly seek the final reference attack altitude of point 15, allowances for missile aerodynamic stability, and for azimuth homing maneuvers are made, and a maximum dive angle of 15 from the horizontal is imposed upon the craft. The missile dives at this maximum angle until the altitude of point 13 is reached. At this much lower altitude, approximately 1500 feet for this specific embodiment, the autopilot in response to the difference of the altimeter and first reference signals directs the missile to gradually pull out of its 15 dive in a uniform manner. For example at altitudes of approximately 1400 feet the missile dives at a 14 angle, at 1300 feet at a 13 angle etc. During this pull out of the missile reaches an altitude represented by point 14. By this time the craft has completed most of its drop from the high release altitude and is relatively close to the final reference attack altitude of point .15, and also to the Water surface, and it is now desired that the missile quickly reach the final reference altitude and stabilize about this altitude. Accordingly, at the altitude of point 14 additional autopilot circuits (gain switch) respond to the altimeter signal and bring about two operations. in the first, the low altitude reference signal with which the altimeter signal is compared to derive the altitude error, is changed from altitude reference 1 corresponding to the altitude of point 16 to the final reference corresponding to the higher altitude of point 15. This first operation is carried out to prevent the missile in its dive from altitude point 14 from overshooting its former reference 1 and diving into the water. In the second operation at point 14, the autopilot circuits are made more sensitive to the altitude and final reference difierence error signal permitting the missile to quickly reach the final reference altitude of point 15 and stabilize about this altitude, as may be seen from FIG. 1. After the missile reaches altitude point 14, and the above-mentioned effects take place, the maximum dive or climb angles allowed the missile in response to altimeter and new reference error signals are still limited to allow for missile azimuth maneuvers while homing on the target, but the increased sensitivity provided permits a response of the missile to altitude correction commands approximately ten times as great as that taking place during the altitude program prior to the gain switch being thrown at altitude point 14. After the missile has reached the final reference attack altitude point 15, it stabilizes about this reference altitude while continually homing on the target in azimuth as before, and when approaching the target and a given predetermined range therefrom is reached, it releases an explosive charge or payload, such as a sonic homing torpedo (shown at point 17) which thereupon enters the water and directs itself at the target 20 by its own propulsion and its own homing guidance, as is well-known to the art.

The illustrated altitude path 12 of HG. 1 is not intended as a scale representation of the distances traveled by the missile from the point of release 8, until releasing the sonic homing torpedo 1'7, for assuming the missile is released at a 20 mile range from the target, the major portion of this 20 mile attack path occurs at the low level final reference altitude of point 15, shown by the broken line representation. Therefore, in FIG. 1 the path from altitude point 8 to altitude point 16 is purposely expanded in relative length for purposes of showing the various phases of the preferred dive program when the missile is released at the maximum allowable altitude.

Referring now to FIG. 2 showing in block diagram form the preferred overall autopilot circuits, two command signals directing the autopilot circuits to control the missile, one from the altimeter (not shown) and. the other from the missile radar (not shown), are sent in on lines 21 and 44 respectively. The autopilot circuits receiving these command signals, as may be seen from FIG. 2, may be generally broken down into two groups A and B. Each of these groups of circuits are shown enclosed by a dotted line, group A being responsive to the altimeter signal from line 21, hereinafter to be called the Elevation Channel of the autopilot, and group B being responsive to the azimuth command signal from line 44 hereinafter to be referred to as the Azimuth Channel of the autopilot. Each of the above-mentioned autopilot channels comprises in essence a servo slaving arrangement to compel the missile heading to follow the command signals. That is, the Elevation Channel A circuits slave the missile elevation heading to the altimeter to minimize the above-mentioned altitude error, and the Azimuth Channel B circuits slave the missile azimuth heading to the missile radar to minimize the radar azimuth error signal. Each of these channels are responsive independently to their respective command signals, but their outputs cooperate and act simultaneously in effecting the desired missile heading providing for unison movements of the missile elevons and differential movements of the elevons to bring about changes in elevation and azimuth heading respectively.

In the Elevation Channel designated A, the altimeter signal indicative of missile altitude is sent in over line 21 to an altitude reference compensator 22. The altitude reference compensator operates in three distinct modes in response to the magnitude of received signals. For all large altimeter signals representative of missile altitudes above point 13 of FIG. 1, this device generates a fixed signal representative of altitude reference 1 (point 16 of FIG. 1) and subtracts this fixed signal from the altimeter signal to generate the above-mentioned altitude error, while limiting the generated altitude error signals for all altitudes above point 1'3 of FIG. 1 to the magnitude of error signal generated at point 13. In the second mode taking place for missile altitudes between points 13 and 14, the fixed generated signal representative altitude reference 1 is subtracted from the altimeter signal to generate a true altitude error, and in the third mode taking place for all altimeter signals representative of missile altitudes below point 14 of FIG. 1, this device generates a fixed signal representative of the final reference altitude oint 15 of FIG. 1) and sub tracts this fixed signal from the altimeter signal to yield an altitude error, signal, and amplifies this error signal (more correctly eliminating attenuation present in the first mode). In the second and third modes no limiting is imposed on the altimeter error signal by the altitude reference compensator circuit, leaving the output signal of compensator 22 directly responsive to the deviation of missile altitude from the first and final reference altitudes respectively, however, the error signal in the third mode is amplified to provide increased sensitivity of the autopilot to the error signal.

The altitude error signal is then conducted to the elevation summation amplifier 24 over line 23 where the error signal is amplified, and further limited (4%) for allowing stability and azimuth control of the missile as will be more completely comprehended from subsequent discussions, and the resulting signal output of 48 is then sent to the longitudinal control summation amplifier 32 and limiter 63 for further voltage amplification. The twice voltage amplified and limited altitude error signal is then sent out over lines 33 and 34 in opposite phase, as shown, to the port and starboard servo amplifiers, where the input signals are power amplified to drive the port and starboard actuators 37 and 56 respectively. These servo amplifiers are of the dilferential type wherein application of like polarity signals to corresponding 55 which energize the port and starboard actuators, driving the port and starboard elevons respectively, so that these elevons are moved in unison and in like direction to bring about changes in the missile elevation heading. Of course, as the Elevation Channel A neglecting the limiting devices comprises pure linear amplification, the amount of this unison elevon movement is directly related to the altitude error comprising the difference between the altimeter signal and the particular reference signal employed.

Movement of the elevons 39 and 58 causes to be generated on lines 28 and 29 respectively, feedback voltages in opposition to the commanding signal on lines 27 feedting the longitudinal control summation amplifier 32. These voltages are generated by two energized potentiometers 61 and 60 respectively, whose variable center taps are mechanically ganged to elevons 39 and 58 respectively, such that if it be assumed that movement of both elevons 3 and 58 upward moves center taps of potentiometers 6'1 and 60 to the left, and downward to the right, it is seen that signals of like polarity are generated on lines 28 and 29 by unison movement of the elevons in either direction, while two signals of opposite polarity, canceling each other, are produced on these lines by equal differential or opposite direction elevon movements.

For the unison elevon movement as brought about by the- Elevation Channel A of the autopilot in response to the altitude error, these feedback voltages close the servo loop causing it to act as a position slaving device, i.e. the elevons move in like direction until these feedback signals balance the commanding signal on line 27 andthen stop. But as mentioned above like movement of the elevons causes the missile elevation heading tochange and as the missile elevation heading changes a signal is generated by a vertical gyro 40 located within the missile structure, which functions as a standard to generate a signal over line 25 whose magnitude indicates the amount of misssile pitch, and whose polarity indicates the direction of missile pitch from the horizontal. Thus, as the missile responds in elevation heading to the altitude error from the altitude reference compensator, a signal is generated from the vertical gyro in opposition to the altitude error command, telling the autopilot channels that the missile is responding to the command by diminishing the signal on line 27 to the longitudinal control summation amplifier, such that when the missile has assumed the elevation heading angle called for by the error signal, a zero signal over line 27 to the control amplifier 32, directs the elevons to return to their zero position. Thus in effect the altitude error calls for change in elevation heading and drives the elevons to cause the missile direction to vary, until the gyro signals that the missile has assumed the new elevation angle called for, at which time they are returned to zero position and the missile continues along this dive or climb angle until a change in altitude error takes place which drives the elevons to position the missile until its vertical gyro indicates a compliance with the new command.

Autopilot Azimuth Control As discussed above, during this altitude program the missile is simultaneously directed in azimuth to home on the selected target, and signals from the missile radar are continuously sent in over line 44 to the Azimuth Channel B of the autopilot. These signals are conducted to the azimuth signal summation amplifier 47 where they are amplified, and then to limiter 49 where the magnitude of the amplified signal is regulated. The output limited signal is then conducted to the lateral control summation amplifier 51 over line 5t) where further voltage amplification takes place, and the twice amplified signal is then sent in like phase to opposite terminals of the port and stmboard servo amplifiers 35 and 54 respectively, over lines 52 and 53. it will be recalled that this manner of energization, unlike that taking place in the Elevation Channel A, causes differential power amplified signals over lines 36 and 55 to drive the port and starboard elevon actuators in opposite directions and hence cause differential or opposite port and starboard elevon displacements. As the port and starboard elevons 39 and 58 respectively are differentially displaced, two feedback signals of like phase and of magnitude dependent upon the amount of di'lferential displacement are sent back over lines 42' and 43 to the lateral control summation amplifier 51 in the Azimuth Channel in opposition to the amplifier and limiter azimuth command signal on line 59. These feedback signals are taken from the moveable taps of energized potentiometers all and 62 which are mechanically ganged to port and starboard elevons 39 and 58 respectively as in the Elevation Channel. Here it is seen that differential movements of the elevons (i.e. upward movement of elevon 39 moving tap of potentiometer 61 to the left producing a more positive signal on line 42, downward movement of elevon 53 moving tap of potentiometer 62- to the right producing a more positive signal on line 43) are slaved to the amplified and limited azimuth command coming in over line 5%, such that the elevons are differentially displaced until the feedback voltages equal the commanding azimuth signal on line 50. But differential displacement of the elevons causes the missile to roll, slip, and turn, and as the missile rolls a signal is sent out by additional means within the abovementioned vertical gyro standard over line ll whose magnitude is indicative of the amount of roll from the reference attitude and whose polarity indicates the di rection (clockwise or counterclockwise) of roll from the reference. This signal is sent to the lateral control summation amplifier 51 in opposition to the azimuth command coming in over line Stl resulting in a diminishing signal to the elevon actuators as the missile responds to the azimuth command. When the missile rolls to the extent called for by the command in azimuth the differential displacement of the elevons is reduced to zero. As the azimuth command varies the elevons are again displaced until the gyro roll signal indicates the missile has responded to the command.

As noted above, and in the introductory material, the azimuth command signal entering the Azimuth Channel B of the autopilot over line 44, is derived from the missile radar and control system, and this command directs the autopilot to compel the missile to home by pursuit on the target in azimuth. Assuming that lead navigation is now desired, this azimuth command is integrated by devices within the radar and control system and introduced as an additional command to the Azimuth Channel B. This additional azimuth lead command is introduced into the azimuth signal summation amplifier 4-7 input through a summing resistor over line 46, as shown in FIG. 2, and compels the Azimuth Channel B of the autopilot to direct the missile in azimuth to lead the selected target in accordance with the magnitude of this integrated signal.

It should be noted that the feedback from the eleven potentiometers 61, 62, and 6t) due to their polarity of energization act independently for the two autopilot chanels (Elevation and Azimuth). Unison displacement of the elevons in either direction feeds back equal adding or like polarity signals only to the Elevation Channel A, and canceling signals, having no efiect, to the Azimuth Channel B, while differential displacement of the elevons in either direction feeds back equal adding or like poii larity signals only to the Azimuth Channel B, and canceling signals to the Elevation Channel A.

Summarizing, both autopilot channels, the Elevation Channel A and the Azimuth Channel B, simultaneously activate the port and starboard servo amplifiers which control the two elevons of the missile. The lateral control summation amplifier 5-1 of the Azimuth Channel tends to drive the elevons in opposite directions producing a roll and resultant change in azimuth, and the Elevation Channel A of the autopilot drives the servo amplifiers so as to direct the elevons to move in the same direction causing a change in missile elevation heading and resultant change in altitude. The longitudinal control summation amplifier 32 has a limiter 63 such that elevon commanding signals from the Elevation Channel leave a reserve for azimuth maneuvers, while the lateral control summation amplifier fill has no limiting device controlling the output of the Azimuth Channel thereby allowing autopilot azimuth control to take precedence over elevation control when large commanding signals of equal value are simultaneously introduced in both channels. This type of control is desirable to prevent the missile radar from losing sight of the selected target and insuring a homing flight to the target.

Stabilization The above discussion shows in detail the manner in which the autopilot channels control the elevation and azimuth heading of the missile by comparing the present missile heading in elevation and position in roll, as indicated by the vertical gyro, with the desired missile fiight direction as indicated by the altimeter error command and homing azimuth command, and thereafter simultaneously positions the elevons to correct the missile heading to these commands. However, other factors may aifeet the missile heading, tending in some instances to divert its elevation and azimuth direction from the path prescribed by the directing comm-ands. Some of these factors may comprise outside forces such as winds, and other atmospheric conditions, and others may be aerodynamic unbalance of the missile body, or variation of the missile center of gravity caused by diminishing weight of the propelling fuel. Thus, a compensating or stabilizing system is desired to correct for these forces tending to aerodynamically unbalance the missile, or to correct for forces merely tending to divert the missile from its azimuth homing path and preselected altitude program. This stabilization function is performed in part by the vertical gyro located within the missile body and electrically connected in the follow-up paths of the Elevation and Azimuth Channels. As the vertical gyro responds to any missile elevation heading differing from a preset standard or any missile roll differing from a preset standard by generating electrical signals proportional thereto, any undesired missile pitch or roll causes electrical signals indicating these undesired changes to be generated by the vertical gyro in the feedback paths of the autopilot Elevation and Azimuth Channels. These signals are compared with the command signals indicating desired missile heading and a correction is made by positioning the elevons to overcome this pitch or roll and return the missile heading to the desired position.

in addition to this vertical gyro compensation for instability, additional yaw stabilizing means are provided by a gyro stabilized antenna and control system, a complete disclosure of which is found in the related application of Perry R. Stout et al., Serial No. 219,106, filed April 3, 1951, for An Object Tracking Antenna and System of Missile Guidance.

Lead and Lag Networks In all positioning servo or slaving systems a certain amount of compensation is necessary, in some instances for speeding up response, and in others slowing it down to provide the desired response and prevent oscillation.

The present device provides for clevon feedback voltages that are not only indicative of elevon position but that also anticipate elevon movement. This anticipation function has been introduced to prevent elevon oscillation, and as may be seen by reference to FIG. 2 is introduced in the elevon feedback paths 28, 29, .2, and 43 for both the Elevation and Azimuth Channels taking the form of parallel resistor condenser lead circuits 31, 3%, 3%, 3 5b, respectively. An additional lead circuit 31a is. interposed in the gyro roll signal line 41 feeding the lateral control summation amplifier 51 in the Azimuth Channel B where it has been found to aid in roll stability.

Two time delaying networks in the form of T-lag networks are designated 26 and 45 in FIG. 2. These networks are interposed in the pitch input line 25 from the vertical gyro 40, and in the azimuth input line 4-45 from the azimuth signal source respectively, to delay the autopilot elevation and azimuth response to instantaneous error signal changes. As the altimeter response to altitude is relatively gradual as compared with the vertical gyro pitch signal over line 25, this lag network 26 improves pitch stability, and at the altitude point 14 (FIG. 1) when altitude error sensitivity is afiected by approximately a to 1 change, this lag prevents pitch oscillation. The network 27 in the Azimuth Channel B is supplied to prevent a roll oscillation with large azimuth commands, due to the missile inertia."

In the illustrated system, network 26 was supplied with components bringing about a second lag which effectively prevented oscillation at altitude point 14 for a change of l to 10 in altitude error sensitivity.

Detailed Circuitry Before entering into a detailed disclosure of the preferred circuitry employed to perform the above-men tioned functions, it is well to note that for each of the circuits of FIG. 2 in block form, any arrangement of components may be substituted providing they perform the functions above enumerated. For example, each of the signal summation amplifiers 24, 32, 27, and 51, along with limiting means 48, 63, and 49 respectively, may be in the for-m of any type of analogue adding circuit which sums, amplifies, and limits the input signals. The servo amplifiers 35 and 54- may be any type of differential input power amplifier with double ended output, the eleven actuators polarity responsive mechanical positioning devices, etc.

FIGS. 3 and 4 illustrate suitable circuit embodiments for the summation amplifier shown in FIG. 2, the block diagram representation of the overall autopilot system in which the instant invention is to be utilized, FIG. 3 illustrating an azimuth signal summation amplifier circuit 47 and its associated limiter circuit 49 (shown in the block diagram of FIG. 2), and FIG. 4 illustrating a lateral control summation amplifier circuit 51.

Referring now to P16. 3, this circuit generally comprises a two stage D.-C. amplifier, the first stage constituting a plate coupled pentode, and the second stage a triode cathode follower provided with a means for limiting the signal applied to its control grid, and with additional means for generating both a positive and a negative feedback Voltage to the first stage. In the detailed circuit shown, input signals on lines 44 and 46 are introduced to the control grid of pentode electron tube 146 type 5654 of the first stage through a lag network 45 and summing resistor 157 respectively. The screen grid of this tube is energized by a positive voltage taken from a series resistance potential divider connected from the regulated power supply voltage of 300 volts to ground and comprising a fixed resistor of 120K, in series with a variable potentiometer 14-9 of 25K, and fixed resistor 148 of 470K. A positive regulated voltage source of 300 volts energizes the tube plate through a resistance of 560K, and connecting the junction of this resistor and the plate to a regulated minus supply voltage source of 300 volts is a potential divider coupling network comprising three series connected resistors of 680K, 1M, and 1.2M. Across the output of this potential divider comprising the junction point of the 680K and 1M resistors, the plate signal is conducted to the grid of the second stage tube 154- of type 5670 through a high resistance 15d of 1.2M forming part of the signal limiting means. A transient by-pass capacitor of .02 fd. is also connected from the above-mentioned output of the first stage plate potentiai divider to ground. Tube 154 of the second stage is plate energized directly from the common regulatedpositive voltage source of 300 volts, and its cathode energized from the common regulated negative voltage source of 300 volts through an K resistance. Connecting the plate of this second stage tube to ground and also energized by the common regulated positive supply source voltage is a potential divider comprising two series resistors 11.52 and 153 of 270K and 5.5K respectively, whose junction point is connected to the grid of the second stage tube 154 by means of limiter diode connected tube 151 which may as shown comprise the second half of tube 154. The cathode follower output signal to ground is derived from the cathode of second stage tube across a 4.5K resistance, and this signal is conducted to subsequent circuits through resistor 50 of 180K. A feedback line designated 156 also conducts this output signal to the control grid of the first stage pentode 146 through a 2M resistance constituting a negative feedback, and conducts this output signal to the cathode of the first stage tube 146 through a 56K resistance M7 constituting a positive feedback.

The gain of this two stage D.-C. amplifier, due to the positive feedback provided by output line 156, 56K resistor 147, and resistor 1 :8 to the cathode of input tube 146, is relatively high, in the order of 1,000, such that a small positive signal on the grid of input tube 146, results in a relatively high negative signal on output line 5b and feedback line 156, and a small negative signal on the grid of input tube 146, results in a relatively high positive signal ono-utput line 56 and feedback line 156. However, sharp limiting is imposed upon the magnitude of output signal of either polarity by the action of the limiting circuit, comprising high value resistor 150, diode connected electron tube 151 and resistor 153, for large values of positive signals reaching the control grid of output tube 154; and the output tube current cutoff provides the sharp limiting action for all large values of negative signals reaching the control grid of output tube 154. It has been found that the provision of positive feedback in a D.-C. amplifier of this nature allows the overall amplifier characteristics relating output to input signals to approximate a vertical line, that is a small input signal to energize the control grid of the input tube of the output signal to a high value as determined by the limiting devices, thereby approximating the operation of an infinite gain amplifier. The addition of a high value negative feedback resistor 145, connecting the output signal to energize the control grid of the input tube 11 6, in connection with the input summing resistors 45 and 157 allows this device to sum the input signals, and amplify the summed signals in accordance with the ratio of negative feedback resistor to the summing resistors as is well known to the art. Initially with no input energizing voltages, it is desired that the output voltage through K resistor 5t) be low approximating 0 volts, and

thereby indicating to the subsequent autopilot circuits the 'no command condition, however due to the pure resistance coupling provided in the direct current type ampli fier any variation in the value of circuit components such as change in the tube impedances, or change in Value of the circuit resistors caused by heating efiects or aging, may vary this so-called balanced condition or approximate 0 output voltage with no signal, and hence in order to correct for any such undesired effects, a variable balancing resistor 149 of 25K is provided in the screen grid put is needed. For example, three of the summation amplifiers as shown in the block diagram of FIG. 2 may employ single ended devices, and in these units the amplifier circuit of FIG. 3 may be used by merely modifying the component values, and limiting (clipper) circuit as desired, whereas the fourth is required to differentially drive the opposite terminals of the servo amplifiers by means of a double ended output and hence the single ended output circuit of FIG. 3 is not satisfactory. Accordingly FIG. 4 is an illustration of a control summation amplifier embodying the simplified circuit of FIG. 3 in conjunction with additional modifying means for converting the single ended output to a double ended output. Although this illustration relates to the lateral control summation amplifier 51, a consideration of the FIG. 2 block diagram shows that either one or both of the control summation amplifiers may employ double ended output signals for driving the port and starboard servo amplifiers.

Referring now to FIG. 4, the lateral control summation amplifier block representation within a triangular enclos ure designated 51 to conform the representation of FIG. 2, and controlling similar apparatus (not shown in FIG. 10) to that controlled by the amplifier 51 in FIG. 2, is energized by a plurality of input signals through summing lead networks 30a, 30b, and 31a, and through summing resistor i Double ended output lines represented as positive and negative are designated 169' and 52 respectively. Within the enclosure are two cascaded summation amplifiers of the type shown by FIG. 3, the output of the first energizing the input of the second through a 2M summing resistor 167, and also connected to the output of the second by means of two equal series connected resistors of 33K designated 173 and 174. Connecting the series junction of these resistors to ground is a 1.2K resistor 176, and this junction is further connected to the input of the elevation signal summation amplifier 24, equivalent to the amplifier 24 in the Elevation Channel A of FIG. 2, by means of a summing resistor 172.

Input signals energizing the first summation amplifier 165 are added and amplified and the amplified sum is conducted by line 168 to output line 52. This signal is also injected to the input of the second summation amplifier 166 through the 2M summing resistor 167 where it is further amplified by a gain of one, its polarity inverted, and it is conducted to positive output line 169. Hence,

second amplifier 166 provides the means for generating an equal and opposite polarity output signal for the initially summed and amplified signal on line 52. However, if the signal provided by amplifier 166 on line 169 is not equal and opposite to that on line 52, the port and servo amplifiers each energized by one of these lines are driven unequally, wherein the elevons are not differentially displaced by equal and opposite amounts, and a pitch error results. Compensation for this resulting pitch error is made by feeding an error correction signal to the elevation signal summation amplifier 24 through the abovementioned summingresistor 172. This error signal is derived from the mid-point of the series connected resistors 173 and 174, when the potentials on lines 169 and 52 are not equal and opposite, however when these signals are equal and opposite the mid-point of the voltage divider series connected resistors 173 and 174 is at zero potential whereby no error correction signal is transmitted.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A double ended signal summation amplifier comprising two identical single ended, polarity reversing, negative feedback signal summation amplifiers, a coupling resistor, and a center tapped output resistor, the two amplifiers being connected in cascade through the coupling resistor, a negative feedback resistor disposed between the output and the input of the second cascaded summation amplifier, the value of the coupling resistor being equal to that of the negative feedback resistor of the second summation amplifier, the outputs of both amplifiers being connected to energize opposite ends of the output resistor, resistor means disposed between the center tap of the output resistor and ground, and feedback balance compensating means connected to the output resistor center tap to derive an unbalance responsive output for effecting compensation control by applying said last-named output to the input of a control circuit responsive to said double ended amplifier whereby in the absence of a zero voltage output at the compensating means this output represents an error correction signal fed to the control circuit to compensate for the unbalance error in the double ended amplifier.

2. A double ended amplifier comprising two identical single ended, polarity reversing, negative feedback amplifiers, a coupling resistor, a center tapped output resistor, the two amplifiers being connected in cascade through said coupling resistor, a negative feedback resistor disposed between the output and the input of the second amplifier, said coupling resistor having a value equal to the negative feedback resistor of the second amplifier, the outputs of both amplifiers being connected to opposite ends of the said output resistor, a resistor connecting the center tap of said output resistor to ground, and compensating means connected to said center tap to derive an unbalance responsive output for effecting compensation control by applying said last-named output to the input of a control circuit responsive to said double ended amplifier whereby in the absence of a zero voltage output at the compensating means an error correction signal is fed to the control circuit to compensate for the unbalance error in the double ended amplifier.

References Cited in the file of this patent UNITED STATES PATENTS 2,164,402 Guanella c July 4, 1939 2,558,096 Markusen June 26, 1951 2,595,185 Zauderer et al Apr. 29, 1952 2,686,099 Bomberger et al Aug. 10, 1954 OTHER REFERENCES Ragazzini et al.: Analysis of Problems in Dynamics by Electronic Circuits, Proc. I.R.E., vol. 35, No. 7, pages 444 to 452 (May 1947).

Geo. A. Philbrick Researches, Inc.: Catalogue and Manual on GAP/R High-Speed All-Electronic Analogue Computers etc., pages 1 to 5 (copyright 1951). 

